A differential assembly houses a gear assembly that is traditionally configured to change a direction of a power input from a drive shaft to two half shafts. The drive shaft receives power from an engine and through a transmission, while the half shafts deliver power to the wheels from the differential assembly. With reference to FIG. 1, the differential assembly is generally indicated by reference numeral 10. A drive shaft 12 enters a differential assembly housing 14, also referred to as a carrier housing 14, at a front portion 16 of the housing 14. A gear assembly 17, or differential gear set, transfers power to a right half shaft 18a and a left half shaft 18b, which hereinafter are collectively referred to as half shafts 18. The housing 14 also has a plurality of mounting brackets 20 that are configured to secure the differential assembly 10 within the applicable subassemblies (not shown) of the vehicle (not shown).
Based on their construction, solid beam axle housings can be divided into two groups, an integral carrier, or a removable carrier. The integral carrier housing attaches directly to the rear suspension. A service cover, in the center of the housing, fits over the rear of the differential and axle assembly. When service is required, the cover must be removed and the components of the differential unit are then removed. Integral carriers are also commonly referred to as unitized or salisbury-type differentials, named after C. W. Salisbury one of the founders of Salisbury Axle Company.
A removable carrier assembly is configured so that the gearing assembly can be removed from the front of the differential housing as a unit, when the front portion of the differential housing unit is removed. With reference to rear live axles, a rear axle refers an axle mounted in the rear of a vehicle and to the rear tires. The front of the rear axle refers to the area which the driveshaft connects thereto and live denotes that the axle carries power, such as in a rear wheel drive vehicle. The typical housing of a removable carrier assembly has a cast-iron center section with axle shaft tubes pressed and welded into either side. The removable carrier assembly is sometimes called a “banjo” because of the bulge in the center of the housing. The bulge contains the final drive gears and differential gears. In appearance, the two designs of axle housing look similar except that the opening for the differential unit on a banjo axle is at the front and the rear of the housing is solid, while access to the salisbury axle is through a rear service cover.
It will be appreciated that variations of the salisbury and the banjo axles exist, such as independent front and rear axles. With an independent front or rear axle, the differential housing is mounted to the vehicle's chassis. As such, the differential housing does not move with the suspension. The half axles, however, are connected to the wheels of vehicle which are suspended. To that end, constant velocity joints are used to connect the half axles to the differential assembly and the wheel hubs so that the half axles are able to move with the suspended wheels. The differential housing remains unsuspended and secured to the applicable subassemblies of the vehicle.
With reference to FIG. 1 and FIG. 2, the housing 14 further includes a differential assembly cover 22, which attaches to a rear portion 24 of the housing 14 with a plurality of fasteners 26. The rear portion 24 defines a window 24a that provides access to the interior cavity of the housing 14. It will be appreciated that the differential assembly 10 is salisbury differential, as the cover 22 is a separate component that is releaseably connected to the rear of the housing 14. Disposed between the housing 14 and the differential assembly cover 22 is a gasket 28. The gasket 28 seals the differential assembly cover 22 to the housing. By sealing the cover 22 to the housing 14, the gear assembly contained therein is protected from the regime in which it is installed. The cover 22 also forms a sealed volume of space in which the gear assembly is constantly lubricated.
It will be appreciated that the gasket 28 must be placed over the housing 14 in a proper orientation to ensure proper installation when the cover 22 is secured to the housing 14. It will be further appreciated that misalignment of the gasket 28 may lead to improper sealing of the gasket 28, which may manifest itself in leaks from the housing 14. Misalignment may also cause the gasket 28 to be pinched or crimped by the fasteners 26 when the cover 22 is secured to the housing 14. The pinched or crimped gasket 28 may also improperly seal when the cover 22 is secured to the housing 14.
When the cover 22 is secured to the housing 14, the fasteners 26 must be secured so as to apply a clamping force about the perimeter of the cover 22. The clamping force causes the gasket 28 to compress and thus form a seal between the cover 22 and the housing 14. The gasket 28 not only serves to retain the internal lubrication of the differential assembly 10, but also protects the differential assembly from the regimes of driving environment, such as water, salt, and dirt. It will be appreciated that the axle of a vehicle is located along the underbelly of the vehicle and by the very nature of its location is exposed to not just water, salt, and dirt as mentioned above but may also be exposed to high-pressure water from conventional car washes. It will be appreciated that the gasket 28 must not only seal the lubrication in the differential assembly, it must also keep many things out of differential assembly, so water, dirt, salt and the like does not pollute the lubrication.
To that end, an incorrect amount of clamping force applied to the cover 22 may lead to improper sealing of the gasket 28. Over-tightening the fasteners 26, for example, may generate too much clamping force and over compress the gasket 28, such that the gasket 28 may bulge or kink, which is sometimes referred to as coining. Coining and over-compression in general may lead to leaks especially when the gasket expands and contracts due to heating and cooling the assembly 10.
It is desirable, therefore, to secure the differential assembly cover to the housing without a separate compression limiting device. It is further desirable to have the compression limiting device pre-configured into the differential assembly cover. It is also desirable to have a seal pre-attached to the differential assembly cover that is cost-effective and robust. It is additionally desirable to avoid the steps of aligning the gasket while securing the differential assembly cover to the housing.